Sealing mechanism for strapping machines



United States Patent 2,283,947 5/1942 Praemassing...............H 2,958 242 11/1960 Marchant.. 3,194,281 7/1965 Freyet 3,198,218 8/1965 Ericsson etal................

[72] Inventor Larry D. Plunkett Algonquin, Ill. [21] Appl. No. 687,716

Dec. 4, 1967 [45] Patented Dec. 29, 1970 [22] Filed F ORElGN PATENTS 747,766 4/1956 Great Britain................

Primary ExaminerChar1es W. Lanham Assistant Examiner-E. M. Combs Art0rneyEdward R. Lowndes [73] Assignee SignodeCorporation Chicago, Ill.

a corporation of Delaware [54] SEALING MECHANISM FOR STRAPPING MACHINES 2 Claims, 7 Drawing Figs.

[50] Field 72/451, 452; 8l/9.1, 9.1H, 9.1M, 9.11, 301; 140/932, 93.4

[56] References Cited UNITED STATES PATENTS 2,140,658 12/1938 Van Sittert...... 2,223,164 1 1/1940 Childress mechanical advantage for effecting the final compression of the strap between the seal flanges and the crown portion of the seal.

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SEALING MECHANISM FOR STRAPPING MACHINES The present invention relates to package binding tools commonly referred to as strapping tools, and by means of which a loop of flexible metal strapping which has been caused to encircle an article,- or series of articles, is tensioned and thereafter a seal which has been positioned about the overlapping end regions of the loop is crirn'ped or otherwise deformed to provide a seal joint, after which the feed end region of the strapping is severed to free the tensioned loop and the article encircled thereby from the source of strapping. More specifically, the invention is concerned with a novelsealing mechanism which is useable in connection with such strapping tools and by means of whicha pair of composite jaws are caused to close upon a prepositioned seal, which is held thereby, for the purpose of crimping such seal about the overlapping portions of the strapping. A sealing mechanism of this general type is shown and described in U. S Pat. to Ericsson et al. No. 3,l98,2l8,granted on Aug. 3, 1965 and entitled Strapping Tool," and the present: invention is designed as an improvement over such sealing melchanism.

The sealing mechanism of the prese'nt invention is by no means limited to use in connection with heavy duty, portable,

- pneumatically operable strapping tools such as the tool disclosed in the above-mentioned patent vsince the principles thereof may find wide utility in the metal-strapping field, as for example in connection with either large automatic packagehandling equipment, or with small manually operablestrapping tools. Therefore,-the exemplary portable tool subsequently described represents only one environmental disclosure with which the present sealing mechanism may be associated, it being distinctly understood that numerous other environments are-contemplated. Irrespective however of the particular use to which the present invention may be put, the essential features thereof remain substantially the same.

The exemplary tool which embodies the improved sealing mechanism involves in its general organization a base, a frame secured to the base, a gripper for holding the free end of the strap, tensioning means for moving the overlapped portion of the strap relative to the free end, a motor for operating the tensioning means, a magazine for holding a stack of metal seals, opposed coacting composite jaws for applying a seal around the edges of the overlapped portions of the strap and crimping the same, an ejector finger for feeding the metal seals individually and successively to the jaws, a piston-actuated ram for operating the jaws, a cutter blade for shearing the upper overlapped strap portion, and a valve mechanism for operating the tensioning motor and piston-actuated ram. Since the present invention is concerned only with the sealing mechanism of the tool, i.e. the coating jaws and the actuating means therefor, such sealing mechanism has been illustrated and described in detail herein, the remainder of the tool being shown somewhat schematically and only in sufficient detail to render its environmental function clear.

In order to facilitate a clear understanding of theimprovements which have been embodied in the present invention, it is deemed necessary to set forth in some detail the nature and mode of operation of the conventional sealing mechanism which is exemplified by the aforementioned US. ,Pat. No.

3,198,218, similar mechanisms being employed in connection with a wide variety of strapping tools and machines. Briefly, such conventional sealing mechanisms employ a toggle linkage consisting of a pair of upper spreader links having adjacent their upper or proximate ends pivotally connected to a vertically movable piston actuated ram, and having their lower or distal ends pivotally connected to the upper ends of respective jaw members. The jaw members are pivoted medially of their ends for swinging movement in unison and in opposite directions, the lower ends of such members constituting jaws proper which move toward each other for seal crimping purposes under the influence of the spreader links as the ram descends during the power stroke of the piston. As the jaws move inwardly toward each other, an initial wrapping of the seal about the overlapping portions of the strapping takes place, this operation entailing little or no pressure of the seal upon the strapping. Continued inward movement of the jaws results in a terminal application of high pressure to the strapping along the edge regions thereof as these edge regions become compressed between the seal flanges and the crown portion of the seal. Where relatively wide steel strapping is concerned the jaws are usually'of a composite sectional nature and reaction anvil members, commonly referred to as notcher blocks, are interposed between adjacent jaw sections and rest against the crown portion of the seal while the intervening jaw sections force the steel laminae consisting of increments of the seal flanges, the" edges of the steel strapping, and overlying increments of the seal crown upwardly between adjacent notcher blocks so as to displace a series of two or more spaced-apart offset tabs or ears out of the general plane of the flattened seal, thereby positively interlocking the overlapping portions of the strapping so that there can be no slippage. Such notching" of the seal and its contained strapping invariably requires a high terminal application of pressure to the seal by the opposed crimping jaws.

Sealing mechanisms of the type briefly outlined above are possessed of certain limitations, a principal limitation residing in the fixed correlation between the movement of the ram and the swinging seal crimping jaws proper. Because the toggle linkage mechanism involved embodies fixed pivot points between each pairof adjacent links, each increment of jaw closing movement is necessarily accompanied by a corresponding increment of ram movement. Thus, the ram is obliged to travel downwardly an appreciable distance during its power stroke in order to effect wrapping of the seal about the strapping, and to travel an additional distance in order to effect the terminal or final seal notching operation, full power being applied to the ram-actuating piston during its entire power stroke. As a consequence, not only is a relatively long power stroke required, thus necessitating a fairly massive piston and cylinder arrangement, but additionally large quantities of air are consumed in operating the tool. Furthermore, such an arrangement involves the use of relatively long links in the linkage system, thus further contributing toward overall massive tooldesign.

The present invention is designed to overcome the above noted limitation that is attendant upon conventional sealing mechanisms for strapping tools and, toward, this end, the invention contemplates the provision of a novel sealing mechanism wherein, instead of the usual toggle joint connection between the jaw-actuating ram and the jaw members,

there is employed a wedge member which is carried by the shorter ram stroke is made possible due to the elimination of the usual spreader links which are requisite to a toggle action.

Thus, in the case of a pneumatically operable strapping tool, the small piston displacement involved in moving the ram leads to a reduction in the height or surface area of the piston chamber or cylinder and a consequent reduction in overall tool size, as well as 'a reduction in weight. The elimination of toggle spreader links further contributes toward compactness of tool design. In the case-of manually operable strapping tools, a reduction in ram stroke or effort gives the tool designer a choice of employing a shorter eccentric stroke for driving the ram so that a shorter operating lever stroke may be employed, or of attaining the same power with a shorter members, the shape of the wedge member being such that during initial descent of the ram a relatively fast jaw-closing movement is attained, this movement resulting in a folding or wrapping of the seal flanges about the overlapping portions of the strapping. This initial fast jaw movement is followed by a slow terminal jaw movement during which the thus folded seal flanges are acted upon by the jaws to effect compression of the strapping between these flanges and the crown portion of the seal, such compression being accompanied, if desired, by a notching of the seal edges as heretofore described. Since the initial fast jaw movement takes place when jaw loading is relatively light, and the terminal slow jaw movement takes place when jaw loading is relatively heavy, the application of reaction thrust to the ram during its descent is to a large extent equalized or, in other words, the ram effort curve" as it is sometimes referred to, is rendered more uniform. Thus, in the case of a hand-operated strapping tool, not only is a shorter lever stroke adequate to effect the entire crimping cycle including both seal wrapping and seal notching, but no sudden increase in reaction force is encountered so that jerking move- I mentsof the operating lever are avoided. In the case of poweractuated tools, the absence of a sudden increase of reaction force to continued downward movement of the ram and its associated piston results in a smoother and more silent operation of the tool during the crimping cycle.

The provision of a sealing mechanism for strapping tools such as has briefly been set forth above and possessing the stated advantages constitutes the principal object of the present invention. Numerous other objects and advantages, not at this time enumerated, will readily suggest themselves as the following description ensues.

In the accompanying three sheets of drawings forming a part of this specification, one illustrative embodiment of the invention has been shown.

In these drawings:

FIG. 1 is a side elevational view of a pneumatic strapping tool embodying the improved sealing mechanism of the present invention;

FIG. 2 is a bottom plan view of the structure shown in FIG. 1;

FIG. 3 is a sectional view taken substantially on the line 3-3 I of FIG. 1 and showing the seal crimping jaws in their fully retracted position and at a point in the operating cycle immediately following the feeding of a seal thereto;

FIG. 4 is a fragmentary sectional view similar to FIG. 3, showing the seal-crimping jaws in the position which they assume after the wrapping portion of the crimping cycle has been completed and immediately prior to the notching operation;

FIG. 5 is a sectional view similar to FIG. 4, showing the crimping jaws in their final closed position after the notching operation has been completed;

FIG. 6 is a fragmentary exploded perspective view of a ram release mechanism employed in connection with the invention; and

FIG. 7 is a fragmentary sectional view taken substantially on i the line 7-7 of FIG. 2.

Referring now to the drawings in detail and in particular to FIGS. 1 and 2, an exemplary form of pneumatic-strapping tool embodying the improved sealing mechanism of the present invention has been designated in its entirety at 10. This strapping tool is of the general type shown and described in the aforementioned US. Pat. to Ericsson et al. No. 3,198,218 and only such portions of the tool as contribute toward an understanding of suitable environment for the present sealing mechanism have been illustrated herein, these portions being only briefly described. For a full understanding of the nature and operation of the illustrated tool 10, reference may be had to such patent.

Briefly, the tool 10 involves in its general organization a base frame or foot assembly 12 to which a handle 14 is secured, the latter extending upwardly and forwardly from the front end of the foot assembly and terminating in a suspension hook 16 which overlies the center of gravity of the tool and by means of which the tool as a whole may be suspended from an overhead adjustable convenience cable (not shown). The base 12 is provided with a flat bottom surface 18 (FIG. 2) adapted to be supported on the article undergoing strapping and it is formed with a pair of spaced wings 20 and 22 which project laterally from one side of the base and provide a gap or void 24 therebetween which is sufficiently long as to permit entry of the jaws associated with the sealing mechanism of the present invention for the purpose of crimping a metal seal such as that shown at S in FIG. 3 around the overlapped portions of a flat metal strap and thereby securing the seal in position on the strap so that it assumes the condition in which it is shown in FIG. 5.

The sealing mechanism which will be described in detail presently, has been designated in its entirety at 30 and the stacked seals S are fed thereto from a magazine 32 by means of an ejector arm 34 (see also FIG. 7) which engages the lowermost seal in the stack and pushes the same between the opposed seal crimping jaws associated with the sealing mechanism 30, all in a manner that will be made clear presently. Both the ejector arm 34 and seal magazine 32 are supported on a main frame or casting, various portions of which appear in FIGS. 1 and 2 and which have been severally designated at 36. The frame is secured by cap screws 38 to the foot assembly 12. The main frame 36 also serves to support a combined valve and cylinder housing 40 which provides a cylinder section 42 and a valve section 44. The cylinder section 42 bears a direct relation to the present sealing mechanism 30, this relation being set forth in detail subsequently. The valve section 44 however is only indirectly related to the sealing mechanism and therefore the details thereof have not been illustrated. It is deemed sufficient for purposes of disclosure herein to state that the valve mechanism is effective under the control of a pair of levers 46 and 48 to perform certain control functions, among which are initiating the strap tensioning operation and initiating the strap-sealing and shearing operation.

At the front of the base frame 12, an integral support 50 projects upwardly and carries a transverse rock shaft 52 to which there is secured a tiltable frame 53 on which there is mounted a pneumatically operable-tensioning motor 54. A feed wheel 56, carried on a shaft 58 cooperates in the usual manner of feed wheel operation with a toothed anvil or backup pad 60 on the base frame 12 which grips the lower overlapping portion of the strap and holds the same fixed while the feed wheel impels the upper portion of the strap in a strap-tensioning direction. The shaft 58 is carried on the frame 53 at a region below the level of the rock shaft 52 so that when rocking movements are imparted to the frame about the axis of the rock shaft 52 the feed wheel 56 may be raised and lowered out of and into cooperation with the backup pad 60 while at the same time the tensioning motor will be moved between a lowered and a raised position. Releasable latch means (not shown) is provided for maintaining the tiltable frame 53 in its inoperative position wherein the feed wheel 56 is raised from the strapping while a spring encircles the rock shaft 52 and yieldingly biases the frame 53 toward its operative position of feed wheel engagement with the strapping. At the rear end of the tool a depressible spring biased lever 62 controls the raising and lowering movements of a rear-toothed gripper element 64 (see also FIG. 7), the latter serving to anchor the free end of the strap at the time of initial loading of the tool.

After the sealing mechanism 30 has been operated to effect crimping of the seal S about the overlapping portions of the tensioned loop of strapping, a cutter blade 66 which is carried by a movable sealing unit proper 70 and which moves bodily therewith, is caused to descend against a fixed cutter block 72 to effect shearing of the free end portion of the strapping to thus free the tensioned loop of strapping so that the strapped article may be removed from the strapping tool.

The arrangement of parts thus far described is purely conventional and no claim is made herein to any novelty associated with the same, the novelty of the present invention residing rather in the construction and operation of the sealing mechanism 30 which will now be described in detail.

Referring now additionally to FIGS. 3, 4 and 5, the sealing mechanism 30 of the present invention is operable under the control of a vertically movable ram 100 associated with the cylinder section 42 of the housing 40 and which is provided with a stem portion 102 and an enlarged head portion 104. The stem portion 102 is fixedly secured to a piston 106 which is disposed within a cylinder proper 108. The stem portion 102 of the ram 100 projects through the bottom wall 110 of the cylinder, the head portion 104 being disposed externally of the cylinder 108 and being slidable in a vertical bore 112 provided in ajaw support 114.

The head portion 104 of the ram 100 is recessed as at 116 on opposite sides thereof for a purpose that will be made clear presently, and the lower end of the head portion below the recesses is tapered so as to provide downwardly and inwardly sloping sides 117 which are curved on a relatively long radius and which merge as shown at 118 with the bottom of the ram on a relatively short radius. These sides constitute operative cam surfaces which cooperate in the manner of a wedge with a pair of composite seal-crimping jaw members 120 to impart seal-crimping movements thereto inf a manner that will become clear presently. This lower portion of the ram also is formed with flat parallel sides 122 which do not affect the sealing function of the jaws. In order to facilitate subsequent description, this lower tapered portion of the ram 100 will be referred to as the wedge part and it has been designated in the various views of the drawings at 124.

The jaw support 114 is formed with a depending side plate 123 (see also FIGS. 1 and 7) which, in combination with the aforementioned cutter blade 66, establishes a cagelike enclosure for the two jaw members 120, as well as for certain other operative instrumentalities associated with these jaw members and which will be described subsequently. The cutter blade 66 is secured to the jaw support 114 by means of an integral square lug or pilot boss 125 (FIG. 7) which projects into a square opening 126 in the cutter blade and which serves to maintain the cutter blade and its attached jaw support 114 in an erect condition and to guide the same in their vertical path of movement. A spline connection 128 is provided between the cutter blade and the adjacent wall of the seal magazine 32 and further assists in the guiding function. 7

As best seen in FIGS. 6 and 7, the head portion 104 of the ram 100 is formed with a tangentially extending notch 130 in its outer surface, this notch being designed for cooperation with a cam latch 132 in the form of a rock shaft which is mounted in the jaw support 114.'The latch 132 is recessed medially of its ends as shown at 134, thus providing an edge I 136 which is engageable in the notch 130 under the influence of a biasing spring 138 (FIG. 1) in order to latch the jaw support 114 and ram 100 together for movement in unison. One end 140 of the cam latch 132 projects outwardly of the jaw support 114 and has a flattened surface 142 designed for engagement with a lug 144 secured to a portion of the main casting, such engagement taking place as the cutter plate and jaw support 114 move downwardly in unison. At such time as the cam latch engages the lug, further downward movement of the jaw support 114 is prevented but the angular turning movement of the cam latch 132 incident to such engagement shifts the edge 136 of the latch out of the notch 130 in the ram 100, thus freeing the ram for further downward movement. As will become clear presently, during initial downward movement of the jaw support 114 and prior to the time the cam latch 132 and lug become engaged, the support and cutter blade 66 move in unison and no relative jaw movement takes place, the two jaws serving merely to hold a seal in position therebetween. After latch and lug engagement has taken place, so as to release the ram for further downward movement, an initial downward displacement of the ram relative to the jaw support 114 serves to effect a rapid jaw-closing movement but only to such extent that the seal flanges become wrapped around the side edges of the strapping. Thereafter, continued downward movement of the ram relative to the jaw support serves to effect the terminal-notching portion of the crimping cycle whereby the strapping is compressed tightly between the seal flanges and the crown portion of the seal and the various laminae thus established are notched substantially in the manner set forth in the aforementioned Ericsson U.S. Pat. No. 3,198,218.

Referring again to FIGS. 3, 4 and 5, the provision of the vertically reciprocable wedge part 124 and the manner in which it cooperates with the two jaw members 120 to effect jaw closing movements constitutes the principle feature of the present invention. Each composite jaw member is comprised of a plurality of individual spaced-apart identical jaw sections 148 disposed in parallelism and maintained in their spaced relationship by one or more interposed notcher bars 150. Additional notcher bars 154 lie outside the lateral confines of the jaw members as shown in FIG. 7 and the various interpositioned jaw sections and notcher bars 150 substantially bridge the distance between the cutter blade 66 and the depending side plate 123 of the jaw support 114. It is within the purview of the present invention to vary the number of jaw sections and notcher bars, a greater or lesser number of either being contemplated. However, in the illustrated form, and as best seen in FIG. 7, each composite jaw member 120 is comprised of two jaw sections with two contiguous notcher bars being interposed between these jaw sections and with one notcher bar lying in contiguous relationship on the outer side of each jaw section. It will be understood that by varying the number and disposition of the notcher bars and jaw sections various seal notching characteristics or patterns may be attained.

Each composite jaw member 120 is pivoted intermediate its ends for swinging movement about a horizontal axis by means of a fixed pivot pin 156 which has its opposite ends secured in the cutter blade 66 and side plate 123 respectively. The various notcher bars 150 are identical and each bar has its outer end regions pivotally secured to the opposed composite jaw members by means of free-floating pins 158 which project through the jaw sections] 148 with a loose fit at eccentric points with respect to the pivot pins 156. Clearance slots 160 are formed in the notcher bars 150 for reception of the pivot pins 156 therethrough. The lower end regions of the jaw members 120 constitute jaws proper 162 which are movable toward and away from each other as the jaw members are swung in opposite directions. Small notches 164 are formed in the jaws 162 and facilitate holding of the seals S as they are successively fed from the magazine 32 as heretofore described. It will be observed that as the jaws move inwardly toward each other during any given seal crimping operation, the free floating pins 158 have a large component of downward movement '50 that they carry the various notcher bars downwardly with respect to the jaw support 114. The horizontal component of movement of the pins 158 is extremely small since it depends upon the cosine of the angle involved and therefore there will be no binding of the pins and consequent obstruction to free closing movements of the jaws 162 since the lateral movement of the pins 158 is well within machining tolerances. v

The tapered wedge part 124 is designed for cooperation with a pair of cam follower rollers carried on the upper ends of the jaw members 120, the rollers being disposed between the two adjacent jaw sections and being rotatably mounted on transverse pins 172 which bridge the distance between the two sections. The rollers are of appreciable axial extent, the width thereof being accommodated by laterally offset portions 174 which are provided on the upper ends of the jaw sections. As will be described in greater detail presently, downward movement of the ram 100 relative to the jaw support 114 will cause the wedge part 124 of the ram to enter between the two follower rollers 170 and spread the same (and consequently the upper ends of the jaw members 120) apart, thus eflecting swinging movement of these members in opposite directions and consequent inward movement of the jaw proper 162 toward each other for seal-crimping purposes.

In order to retract the jaws during upward movement of the ram, a pair of tension links 176 which are disposed on opposite sides of the ram having their upper ends pivoted on a pin 178 which projects through the head 104 and establishes a pair of trunnions to which the links are attached. The lower ends of the links are formed with slots 180. one slot receiving therein one of the two pins 172 and the other slot receiving therethrough the other pin 172. The slots are so disposed and are of such length that when the ram head 104 is disposed in the upper region of the jaw support 114 with the cam rod 132 disposed within the notch 130, the lower ends of the slots 180 will support the free-floating pins 172 in such positions that the links 176 and their associated jaw members 120 are coaxial as shown in FIG. 3 with the jaws proper 162 being in their wide open positions. The upper regions of the slots 180 afford clearance for the pins 172 (see H6. 4) so that the jaw members 120 will not be subjected to a toggle action upon descent of the ram.

In the operation of the herein described sealing mechanism, when the piston 106 is at the top of its stroke, the ram will be maintained in the elevated position in which it is shown in FIG. 3 and the jaw support 114 will be raised due to the interengagement between the cam rod 132 and the notch 130. The tension links 176 will maintain the seal-crimping jaws 162 enough to admit a seal S therebetween under the influence of "the ejector arm 34 as previously described. At this time the two follower rollers 170 will make tangential contact with each other so as to determine the precise position of maximum jaw opening. As the ram 100 commences its downward movement, the jaw support 114, together with the entire sealing unit including the jaw members, notcher bars, links and other associated parts, will be lowered bodily as a unit to carry the seal 8 downwardly into a saddlelike position of seating engagement on the overlapping portions of the strapping. During this downward movement, the cutter blade 66 cooperates with the cutter block 72 to shear the upper portion of the strap rearwardly of the region where the seal is immediately thereafter applied. The downward movement of the jaw support continues until such time as the cam rod 132 engages the lug 144 and thus arrests further downward movement of the jaw support and cutter blade while releasing the ram for further downward movement as previously set forth.

As the ram 100 continues its downward movement, the sharply curved cam surfaces 1 18 of the wedge part 124 engage the contiguous follower rollers 170 to initiate the jaw-closing and consequent seal-crimping operation. It will be observed that the wedge part initially engages the two rollers 170 at points which lie on vertical secant planes which pass close to the longitudinal axes of the rollers so that the mechanical advantage tending to spread the rollers apart is small while the resultant initial increment of motion imparted to the rollers is a rapid one. However, since the opposition to jaw-closing movements by the seal S is small at this time, no unduly large counter thrust is offered to the continued downward movement of the ram. It will also be observed that the relation of the two seal flanges to the side edges of the strapping is such that as the jaws 162 progressively move inwardly to effect the seal-wrapping operation, the amount of bending force required to fold the seal flanges progressively increases as the wrapping operation continues. This is due to a decrease in the length of the seal flanges (i.e. the lever arm) as they wrap themselves around the edges of the strapping. At the same time a corresponding increase in the force exerted by the wedge part 124 as the same enters further between the rollers 170 takes place and, by these phenomena, the aforementioned ram effort curve" is rendered more uniform during the sealwrapping portion of the cycle. Finally, it is to be observed that at such time as the follower rollers 170 have traversed the steep portions 1 18 of the wedge part 124, the seal flanges have been wrapped around the edges of the strapping and further closing movements of the jaws will effect the terminal notching operation.

After the rollers 170 have entered upon the slightly curved cam surfaces 117 of the wedge part 124,11 relatively steep cam angle is involved, thus applying a relatively great spreading force to the rollers 170 which is commensurate with the greater force required for the notching operation. As is the case in the wrapping portion of the crimping cycle, so also in the notching portion of the cycle, the curvature of the cam surfaces 117 is tailored to accommodate the incremental changes of force that are involved in the production of an optimum ram effort curve.

To summarize the above describedtheoretical considerations which are incident to descent of the ram during the crimping portion of the tool-cycle, thecounter force which is applied to the ram incident to the opposition offered by the seal S to the jaws 162 during the crimping operation is equalized over the entire stroke of the rarmby employing a small effective cam angle to increase the counter force and produce a fast'jaw-closing movement during the wrapping portion of the cycle where seal resistance is low, and by employing a large cam angle to decrease the counter force and produce a slow jaw-closing movement during the notching portion of the cycle where seal resistance is high. The counter force is also equalized to a certain extent within the wrapping and notching portions of the crimping cycle by the use of the sharply curved cam surfaces 118 during the wrapping operation and the use of gently curved cam surfaces 117 during the notching operation. The overall result is the attainment of a more linearly straight ram effort curve than has heretofore been possible with the use of toggle linkages for actuating the seal crimping aws.

Return of the seal crimping jaws to their positions of maximum jaw spread to release the crimped seal S and to position them for reception of a fresh seal is accomplished by the lifting action of the tension links 176 as the ram moves upwardly. The lost motion of the pin and slot connections I72, 180 is initially taken up, after which continued upward movement of the ram raises the pins 156 and swings the two jaw members in opposite directions until such time as the two rollers engage each other in tangential relationship. At this time the cam rod 132 again engagesthe notch 132 in the side of the ram head 104 and the jaw support 114 is raised to its uppermost position so that the various parts assume the positions in which they are illustrated in FIG. 3 with the sealing mechanism 30 poised for reception of a fresh seal between the jaws thereof.

In connection with the return or upward movement of the ram 100, it will be observed that no camming pressure whatsoever is exerted by the rollers 170 upon the cam surfaces 117 and 118 of the wedge part 124 of the ram 100. Therefore these rollers are not constrained to rotate during jaw-opening movements. The'only time that rotational motion is imparted to the rollers is during descent of the ram and at such time as the cam surfaces 117 and 118 are forcibly projected between the rollers. As a matter of fact, actual jaw-opening movements do not take place until such time as the pin-and-slot lost motion connections 172, 170 have been fully taken up. By this time, the wedge part 124 of the ram 100 hasmoved above the level and completely out of engagement with the rollers 170. During pin-and-slot takeup movements, the rollers 170 do not follow the contours of the cam surfaces 117 and 118 since they are not motivated to move inwardly toward each other until such time as such takeup movements have been entirely completed. Rotation of each roller 170 is therefore unidirectional, albeit intermittent, and for this reason such bushing or bearing surfaces as may be associated with the rollers 170 and pins 172 are utilized to their fullest extent so that such wear as may take place is unfirmly and coextensively distributed throughout these bearing surfaces. By such an arrangement, and because the rollers 170 are not obliged to reverse their rotation during jaw-opening movements, as would be the case for example with spring-loaded jaws, tool life is greatly extended insofar as the need for bearing replacement is concerned.

The invention is not to be limited to the exact arrangement of parts shown in the accompanying drawings or described in this specification as various changes in the details of construe tion may be resorted to without departing from the spirit of the invention. For example, whereas the downwardly and inwardly sloping side surfaces 117 and 118 on the ram 100 have been shown and described herein as being of curved configuration and on different radii of Curvature, such configuration are merely ones which have proven to be satisfactory in actual practice. Other configurations have also been found to be satisfactory as for example planar surfaces, the only requisite of such cam or wedge surfaces being that the lower surfaces 118 have a wide cam angularity for rapid jaw movement and that the upper surfaces 117 have a sharp cam angularity for slower jaw movement. However, under certain circumstances, as for example where seal notching is not resorted to, it may be found desirable to consolidate these two cam surfaces by substituting therefor a single cam surface of uniform angularity. it is also within the scope of the invention to omit the notcher bars 150 if desired, thus dispensing with any sealnotchingoperation. Furthermore, it is not necessary to employ composite multisection jaw members inasmuch as solid single-piece jaw members may be substituted if desired. Therefore, only insofar as the invention has particularly been pointed out in the accompanying claims is the same to be limited.

lclaim:

1. In a strapping tool, in combination, a seal-crimping unit of the opposed jaw type for crimping an open flange-type seal having a crown portion with depending side flanges about the overlapping portions of a tensioned strapping loop, said unit comprising a jaw support, a ram reciprocable vertically in said support, a pair of jaw members pivoted at spaced points intermediate their ends to said support for free unbiased rocking movement on said support, opposed seal-engaging jaws on the lower ends of said jaw members and movable toward and away from each other between closed and open positions, said jaws, during closing movement thereof, being initially engageable with the seal flanges to effect progressive inward swinging movement and consequent wrapping thereof around said overlapping portions and subsequently to force said seal on the upper end of each jaw member, said rollers, in the open position of the jaws, making tangential contact with each other to thus determine the fully open position of the jaws, a wedge member carried by said ram, movable bodily therewith, and effective during descent of the ram to engage and enter between said rollers to exert a tractional camming and spreading action thereon, thus rocking the jaw members in opposite directions to effect closing movement of the jaws, said wedge member having inwardly sloping cam surfaces adjacent its lower end which engage said rollers simultaneously at points which lie on vertical secant planes in close proximity to the vertical axial planes of the rollers so that immediately after initial engagement of the rollers by the wedge member the rollers are constrained to tractionally roll thereon unidirectionally .and move apart rapidly and effect an initial correspondingly rapid jaw closing movement with relatively low jaw power to bend said seal flanges inwardly toward each other and thereafter, upon continued descent of said ram, said cam surfaces make progressive contact with the rollers at points which lie on vertical secant planes that are progressively removed from said vertical axial" planes, to the end that the rate of separation of the rollers is gradually decreased to effect a correspondingly slow jaw closing movement with relatively high jaw power to effect compression of said overlapping portions of the loop between said flanges and the crown portion of the seal, and a lost motion link connection between said wedge member and the upper end of each jaw member, the effective length of said lost motion link connection being such that during initial upward movement of the ram said connection remains ineffective while the wedge member moves out of tractional contact with the rollers, thus terminating their individual unidirectional rolling1 movement and, during subsequent upward movement of e ram, the connection rs effective to draw the upperends off the jaw members toward each other and restore the jaws to their open positions and means for reciprocating ram.

2. In a strapping tool, the combination set forth in claim 1, wherein said cam surfaces on the wedge member in the extreme lower region of the latter are of wide cam angularity to enhance, by a compounding action, the initial rapid spreading action exerted by the wedge members on the rollers, and in the upper regions of the wedge member are of sharp angularity to enhance the, terminal-slow spreading action exerted by the wedge member on the rollers. 

